https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115005
Bug ID: 115005
Summary: [gcc-13] bogus -Warray-bounds warning
Product: gcc
Version: 13.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: sezeroz at gmail dot com
Target Milestone: ---
Created attachment 58144
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58144&action=edit
reduced C source exhibiting the issue
The attached C source emits bogus -Warray-bounds warnings at -O2 and -O3
(tested on i686 and x86_64):
$ gcc13 -c -O2 -Wall mmcmp-small.c
In function 'block_unpack_8bit',
inlined from 'decrunch_mmcmp' at mmcmp-small.c:231:4:
mmcmp-small.c:155:35: warning: array subscript 4294967295 is above array bounds
of 'const uint32[8]' {aka 'const unsigned int[8]'} [-Warray-bounds=]
155 | if (d >= cmd_8bits[numbits]) {
| ~~~~~~~~~^~~~~~~~~
mmcmp-small.c: In function 'decrunch_mmcmp':
mmcmp-small.c:39:21: note: while referencing 'cmd_8bits'
39 | extern const uint32 cmd_8bits[8];
| ^~~~~~~~~
In function 'block_unpack_16bit',
inlined from 'decrunch_mmcmp' at mmcmp-small.c:229:4:
mmcmp-small.c:90:35: warning: array subscript 4294967295 is above array bounds
of 'const uint32[16]' {aka 'const unsigned int[16]'} [-Warray-bounds=]
90 | if (d >= cmd_16bit[numbits]) {
| ~~~~~~~~~^~~~~~~~~
mmcmp-small.c: In function 'decrunch_mmcmp':
mmcmp-small.c:41:21: note: while referencing 'cmd_16bit'
41 | extern const uint32 cmd_16bit[16];
| ^~~~~~~~~
The original file in question is at
https://github.com/libxmp/libxmp/blob/master/src/depackers/mmcmp.c
I removed as much clutter as I could, but you guys would most probably reduce
it more.
The issue was originally discussed at libxmp:
https://github.com/libxmp/libxmp/issues/667
Notes particularly at
https://github.com/libxmp/libxmp/issues/667#issuecomment-1712584590
The warnings go away if numbits is changed from uint32 to uint8 or uint16:
We had changed it to uint8 as a solution.
